MOSCOW, Russia - A bomb exploded at a college in the Black Sea region of Russian-annexed Crimea on Wednesday, leaving at least 18 people dead and dozens more injured.

The bomb, which went off at a technical college in Kerch, was at first blamed on terrorism by authorities.

According to an initial statement by a Russian national guard official, the incident was a deliberate "terrorist act" caused by an improvised explosive device.

The official was quoted as saying that most of the victims were students of the technical college that has a strength of 850 students.

Adding that a major emergency response operation had been launched and victims had been rushed to local hospitals.

Further, the college director, told Russian reporters that unknown armed men had broken into the building, howeever investigators later debunked this.

Crimea's Russian-backed leader Sergei Aksyonov later told the Russian state TV that an "unidentified explosive device" was detonated at the Kerch-based college by a student, who had killed himself. There were contradictory reports however that stated the victims had died or been wounded by gunshot wounds.

Aksenov debunked other statements and said that reports of a shooting after the explosion that were circulating on social media were untrue.

He said that calm had been restored at the college and later announced three days of mourning for the victims.

Meanwhile, the Investigative Committee later said in a statement that the explosion was caused by an "unidentified explosive device" at the Kerch Polytechnic College.

They added that the bombing killed 18 people and left around 50 others injured near the eastern end of the peninsula that Russia annexed from Ukraine in 2014.

Investigators said that the attack was carried out by a student and wasn't an act of terrorism as earlier suspected.

While initial reports stated that a shrapnel-filled bomb went off in the cafeteria, the Investigative Committee clarified that the victims died from gunshot wounds.

Further, the Investigative Committee said it had re-qualified the charge to mass murder based on its preliminary findings.

As per the Committee's findings, the attacker was identified as 18-year-old Vladislav Roslyakov, a fourth-year student, who killed himself after shooting his victims.

Meanwhile, the Russian Defence Minister Sergei Shoigu said that victims were taken care of and four military planes were ready to evacuate the wounded and military hospital facilities were ready to accept victims if necessary.

Officially part of Ukraine, Crimea was seized by Russia in 2014 and annexed after a disputed vote.

The move was widely condemned by the international community and has since then turned ties between Ukraine and Russia frosty.

Following the attack on Wednesday, Russian President Vladimir Putin's spokesman Dmitry Peskov, said that the President had ordered the Federal Security Service to investigate the explosion.